Abstract: This paper studied the distribution and accumulation characteristics of mineral nitrogen in the soils of different years old apple orchards in dry plateau of eastern Gansu Province. The soil ammonium nitrogen content was increased with the increase of planting year. In the 2-3, 5, 10, 15, 20, and 22 years old apple orchards, the ammonium nitrogen content in 0-120 cm soil layer was 3.3, 5.8, 6.5, 9.1, 12.1, and 15.3 mg·kg^-1, respectively, and 0-60 cm soil layer had a higher ammonium nitrogen content than 60-120 cm soil layer. For all the apple orchards, the nitrate nitrogen content in 0-40 cm soil layer was relatively low, but increased with increasing depth. The soil nitrate nitrogen content also increased with the increase of planting year, which reached 2602.5 kg·hm^-2 in the 0-120 cm soil layer of 22 years old apple orchard. It was concluded that in the apple orchards in dry plateau of eastern Gansu Province, soil ammonium nitrogen was more accumulated in upper layers, while nitrate nitrogen was more accumulated in deeper layers.

Key words: ammonium nitrogen, nitrate nitrogen, distribution, accumulation, apple orchard, forest community, succession, stability, fuzzy mathematics, stand adjustment.